Method for knock regulation in an internal combustion engine

ABSTRACT

The invention relates to a method for knock control of an internal combustion engine, a knock detection being carried out on the cylinders of the internal combustion engine and a moment of ignition being retarded by a specifiable value as a function of detected knocking combustion in at least one of the cylinders, the system including at least two evaluation electronics and at least one cylinder being assigned to each of these evaluation electronics, and the knock sensor signals assigned to the cylinders being evaluated by the evaluation electronics assigned in each case, and the knock detection and the specification of the moment of ignition being effected by a control electronics, and the evaluation electronics being monitored for functionality.  
     It is provided that, upon detection of a malfunction of at least one of the evaluation electronics ( 30 ), the at least one cylinder ( 12, 14 ) assigned to this evaluation electronics is linked to the control of at least one cylinder having intact evaluation electronics ( 32 ).

[0001] The present invention relates to a method for knock control in aninternal combustion engine having the features named in the preamble ofclaim 1.

BACKGROUND INFORMATION

[0002] Carrying out a so-called knock control in internal combustionengines is known in the art. In so doing, a combustion process in thecylinders of the internal combustion engine is monitored for knockingcombustion. Knocking combustion is identified by characteristicvibrations that may be detected using so-called knock sensors which aremounted on the housing of the internal combustion engine. Knockingcombustion is, for example, a function of the quality of a fuel beingused, the compression of the fuel/air mixture in the cylinders and/orthe moment of ignition. The ignition timing is retarded by a specifiableamount as a function of the detected knocking combustion. Sinceretarding the ignition timing leads to loss of torque and increased fuelconsumption, running the internal combustion engine as close as possibleto a so-called knock limit is known in the art. The knock control inthis case runs the internal combustion engine as close as possible tothe knock limit. Here, the ignition timing is controlled according tothe actual signals determined by the knock sensors.

[0003] Detecting knock using knock sensors, which are typically designedas structure-borne noise sensors, is known in the art. The use of ioniccurrent sensors or pressure sensors is also conceivable. At least onecylinder of the internal combustion engine is assigned to each of theseknock sensors. The control unit has two evaluation electronics to whichthe sensors are assigned, and by which the sensor signals are evaluatedin a cylinder-specific manner. The evaluation circuit supplies theresult of the preprocessed sensor signals to a control electronics,which typically is integrated within an engine control unit. Here,knocking of the individual cylinders is detected, and the ignition angleretard and moment of ignition are calculated.

[0004] During normal use of the knock control, the evaluationelectronics are continually monitored for correct functioning by adiagnostic. If a malfunction is determined, the system automaticallyswitches to safety knock control to prevent damage to the internalcombustion engine. This safety knock control provides that of a safetyretard of the ignition timing is implemented for all cylinders of theinternal combustion engine. However, in this context, it isdisadvantageous that whenever the moment of ignition, and thus theignition angle, is retarded away from the optimal ignition angle, theefficiency and the power output of the internal combustion engine arereduced, thereby increasing fuel consumption. In turbo-charged internalcombustion engines, retarding the moment of ignition may cause thecharging-air pressure to drop, which can lead to power losses of up to40%.

ADVANTAGES OF THE INVENTION

[0005] The method according to the present invention having the featuresmentioned in claim 1 offers the following advantage: in the event of afailure or malfunction of an evaluation electronics of the knockcontrol, a safety retard of the moments of ignition is not necessary forall cylinders of the internal combustion engine. Since, upon detecting amalfunction of at least one of the evaluation electronics, the at leastone cylinder assigned to this evaluation electronics is linked to thecontrol of at least one cylinder with intact evaluation electronics, allcylinders of the internal combustion engine are advantageously notautomatically switched to the maximum safety retard, but rather the atleast one cylinder to which the malfunctioning evaluation electronicscircuit is assigned is guided by another cylinder of the internalcombustion engine whose evaluation electronics is in working order. Thisensures that the cylinders with operational evaluation electronics maystill be operated using an optimal moment of ignition, while only the atleast one cylinder with malfunctioning evaluation electronics isoperated with retarded ignition timing which, however, is below thepreviously known safety ignition retard. The overall result is that theefficiency of the internal combustion engine is only insignificantlyimpaired. In particular, this guidance of the cylinder having defectiveevaluation electronics makes it possible to operate the cylinder closeto its knock limit even if its evaluation electronics malfunction.

[0006] If an evaluation electronics circuit fails, a guide cylinderfunction is activated for the cylinders assigned to this evaluationelectronics. This means that the cylinders of the defective evaluationelectronics are guided by cylinders of an intact evaluation electronics.The central control electronics (engine control unit) detects knocking,chooses which cylinders assume guidance of the cylinder assigned to thefailed evaluation electronics, and calculates the resulting ignitionretard. Only if all evaluation electronics are detected as defective isa uniform safety ignition retard activated for all cylinders.

[0007] For the guide cylinder function, at least one cylinder of anintact evaluation electronics is selected as the guide cylinder. Theignition angle settings of the at least one guided cylinder are derivedfrom those of the at least one guide cylinder. This preferably resultsin several possibilities. Thus, an ignition angle setting of the guidedcylinder may be the same as the ignition angle of the guide cylinder.Furthermore, it is preferred if the ignition angle setting of at theleast one guided cylinder corresponds to an ignition angle setting ofthe at least one guide cylinder plus a safety offset (timing retard awayfrom the knock limit).

[0008] Another preferred embodiment of the invention provides that theretard of the ignition angle for the at least one guided cylinder ismade in one step following a knock event at the guide cylinder.Furthermore, it is preferred if the retard for the at least one guidedcylinder is effected in several small steps following a knock event inthe at least one guide cylinder.

[0009] Finally, it is preferable if the cylinder which uses the greatestretard of the ignition timing is established as the guide cylinder.Finally, it is also preferred if, during initialization of the controlelectronics and the evaluation electronics, respectively, it isdetermined which cylinders may be used as the guide cylinder in theparticular groups assigned to an evaluation electronics.

[0010] Preferred embodiments of the invention are yielded from theremaining features indicated in the dependent claims.

DRAWING

[0011] The invention is explained in detail below in an exemplaryembodiment with reference to the accompanying drawing, whichschematically shows a knock control of an internal combustion engine.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0012] The figure schematically shows an internal combustion engine 10,that includes a total of four cylinders 12, 14, 16 and 18. A knocksensor 20, 22, 24 and 26 is assigned to each of cylinders 12, 14, 16 and18. The knock sensors detect structure-borne noise vibrations that arecaused by combustion in cylinders 12, 14, 16 and/or 18. Knock sensors20, 22, 24, 26 are connected to evaluation electronics 30 and 32. Inthis context, evaluation electronics 30 is assigned to knock sensor 20and knock sensor 22, and evaluation electronics 32 is assigned to knocksensor 24 and knock sensor 26. Evaluation electronics 30 and 32 areimplemented using either digital, analog or mixed technology. Evaluationelectronics 30 or 32 are integrated within an engine control unit 28 towhich are fed the signals supplied and preprocessed by knock sensors 20,22, 24, 26. Engine control unit 28 includes, among other things, atleast one microprocessor 33 and at least one memory medium 34 in whichcontrol algorithms for components 36 that influence the combustion incylinders 12, 14, 16 and 18 are stored. Components 36 are, for example,final controlling elements for adjusting an ignition of internalcombustion engine 10.

[0013] A diagnostic module 38 is assigned to evaluation electronics 30and 32 and permanently monitors the functionality of evaluationelectronics 30 and 32 during their specified use. Diagnostic module 38is implemented in engine control unit 28. The diagnostic module may beimplemented physically by the at least one microprocessor 33 thatprocesses an appropriate routine.

[0014] The knock control schematically depicted in the Figureillustrates the following function:

[0015] During the operation of internal combustion engine 10, thecombustion in individual cylinders 12, 14, 16 and 18 is continuallymonitored via knock sensors 20, 22, 24 and 26. According tostructure-borne vibrations picked up in this context, a controlparameter is specified for components 36 via evaluation electronics 30and 32 and data control unit 28, so that knocking combustion incylinders 12, 14, 16 and 18 is suppressed. Using the control parameters,cylinders 12, 14, 16 and 18 in this case are operated close to theirknock limit.

[0016] Evaluation Electronics 32 and 34 are continually monitored forfunctionality by diagnostic module 38 (control unit 28). If there is amalfunction, for example, in evaluation electronics 30, it is detectedby diagnostic module 38. Then diagnostic module 38 causes a guidecylinder function to be activated for the knock control of cylinders 12,14. In this way, cylinders 12, 14 are guided by the cylinders assignedto evaluation electronics 32. Due to this measure, cylinders 16 and 18continue to be operated with optimum knock control via evaluationelectronics 32. Simultaneously, a guide cylinder function is activatedfor the knock control of cylinders 12, 14 so that they also continue tobe operated in knock-controlled fashion. The overall result is thatcylinders 16 and 18 are run with optimal knock control, while cylinders12 and 14 may be operated relatively close to their knock limit, despitea defect in evaluation electronics 30, assigned to them. Cylinders 12and 14 are thus guided by cylinders 16 and 18. Due to this guidance,none of cylinders 12, 14, 16 and 18 of internal combustion engine 10have to be driven using the safety retard of the ignition timing and besubject to the related previously-mentioned disadvantages. The overallresult is a clear improvement in power output and efficiency of internalcombustion engine 10 when evaluation electronics 30 is defective.

[0017] According to additional exemplary embodiments (not shown), eachof cylinders 12, 14, 16 and 18 may obviously be assigned its ownevaluation electronics that may correspondingly be switched over in theevent of a fault. Also, for internal combustion engines 10 that havemore then four cylinders, corresponding cylinder groups may each beassigned to an evaluation electronics.

[0018] Furthermore, it may be provided that not every cylinder 12, 14,16, 18 is monitored via its own knock sensor 20, 22, 24, 26. In thiscase, one knock sensor may also be assigned to a plurality, for example,two cylinders.

What is claimed is:
 1. A method for knock control of an internal combustion engine, a knock detection being carried out on the cylinders of the internal combustion engine and a moment of ignition being retarded by a specifiable value as a function of detected knocking combustion in at least one of the cylinders, the system including at least two evaluation electronics and at least one cylinder being assigned to each of these evaluation electronics, and the knock sensor signals assigned to the cylinders being evaluated by the evaluation electronics assigned in each case, and the knock detection and the specification of the moment of ignition being effected by a control electronics, and the functionality of the evaluation electronics being monitored, wherein, upon detection of a malfunction of at least one of the evaluation electronics (30), the at least one cylinder (12, 14) assigned to this evaluation electronics is linked to the control of at least one cylinder (16, 18) having intact evaluation electronics (32).
 2. The method as recited in claim 1, wherein at least two cylinders (12, 14, 16, 18) are assigned to an evaluation electronic evaluations (30, 32), and, in the event of a failure of one of these evaluation electronics (30), the cylinders (12, 14) assigned to them are guided by cylinders (16, 18) of a different evaluation electronics(32).
 3. The method as recited in one of the preceding claims, wherein at least one cylinder (16, 18) is used as a guide cylinder, and from the ignition angle or timing retard of the at least one selected guide cylinder (16, 18), an ignition angle is specified from which the ignition angles of the guided cylinders (12, 14) are derived.
 4. The method as recited in claim 3, wherein the ignition angle, i.e. the timing retard of the guide cylinder (16, 18) is used for the guided cylinders (12, 14).
 5. The method as recited in one of the preceding claims, wherein a retard of the ignition angle is effected for the guide cylinder (16, 18) and for the guided cylinders (12, 14) in response to a knock event in a guide cylinder (16, 18).
 6. The method as recited in one of the preceding claims, wherein a safety offset away from the knock limit is applied to the ignition angle of the at least one guide cylinder (16, 18) to determine the ignition angles of the guided cylinders (12, 14).
 7. The method as recited in one of the preceding claims, wherein the ignition timing of the guided cylinders (12, 14) is retarded in several small steps following a knock event in the guide cylinder (16, 18).
 8. The method as recited in one of the preceding claims, wherein the ignition timing of the guided cylinders (12, 14) is retarded in a single step following a knock event in the guide cylinder (16, 18).
 9. The method as recited in one of the preceding claims, wherein the cylinder that has the largest, the smallest or an average retard of the ignition angle is used as a guide cylinder (16, 18).
 10. The method as recited in one of the preceding claims, wherein the cylinder that is determined in an initial setting (application) of the ignition system is used as guide cylinder (16, 18). 